Production of 1:1:3-trialkoxyprop-2-ene



United States Patent PRODUCTION OF 1:1:3-TRIALKOXYPROP-2-ENE Reginald Harold Hall, Sutton, and Archibald Robert Graham, Richmond, England, assignors to The Distillers Company Limited, Edinburgh, Scotland, a British company No Drawing. Application December 29, 1954 Serial No. 478,516

Claims priority, application Great Britain January 13, 1954 9 Claims. (Cl. 260-615) The present invention relates to a process for the production of 1 :1s3-trialkoxyprop 2-enes.

According to the present invention the process for the production of a 1:1:3-trialkoxyprop-2-ene comprises reacting a 1:l:3-trialkoxy-2-halopropane with an alkali metal alkoxide of 4-8 carbon atoms in solution in an alkanol of 48 carbon atoms, the alkoxide and the alkanol each having a straight chain of at least 3 carbon atoms.

The 1:1:3-trialkoxy-2-halopropanes used as starting materials in the present invention are suitably prepared from acrolein by the steps of reacting it with an aqueous hypo-halogenous acid, for instance with an aqueous solution of chlorine or bromine, distilling the product in the presence of steam and thereafter reacting the formed ahaloacrolein with an alkanol in the presence of an acid catalyst to form the acetal.

It has been found that the crude mixture of acetals produced in this manner can advantageously be employed in the process of the present invention.

Preferably the alkali metal alkoxide is employed as a solution in the corresponding alkanol and preferably also this corresponds to the alkoxy groups in the starting material. According to a preferred embodiment of the invention an alkali metal butoxide is employed and it has also been found that the potassium alkoxides react more quickly than the sodium compounds.

According to a further preferred embodiment of the invention l:1:B-tri-n-butoxyprop-Z-ene or 1:1:3-triisobutoxyprop-Z-ene is prepared by the dehydro-chlorination of the corresponding 1:1:3tributoxy-2-halopropane with potassium n-butoxide in n-butanol or potassium isobutoxide in isobutanol respectively at a temperature of about 120-130 C.

The use of the specified alkoxides in solution in the corresponding alkanol permits the use of reaction temperatures in excess of about 100 C. without recourse to the use of pressure. contains suspended inorganic salts and the use of the specified alkoxides allows the step of water washing of the product as hereinafter described.

The dehydrohalogenation of the 1:1:3-trialkoxy-2-halopropane in accordance with the present invention is suitably carried out at an elevated temperature, for example l00160 C. and preferably of about 120-140 C. Suitably the 1:1:3-trialkoxy-2-halopropane and the alkali metal alkoxide in solution in-the corresponding alkanol are mixed together and heated to an elevated temperature of about 120140 C. for instance a 100% excess, in order to obtain a reasonable reaction rate.

The reaction product contains suspended inorganic Moreover the reaction mixture.

In practice an excess, of the alkoxide is necessary 2,870,221 I Patented Jan. 20, 1959- halide as well as excess alkali metal alkoxide and according to the preferred embodiment of our invention the trialkoxypropene is isolated from the reaction product by the step of treating the mixture with a limited amount of water so that all the metal halide dissolves and a separate aqueous phase is formed, and recovering the trialkoxypropene from the alcohol phase. The alkali metal alkoxide is hydrolysed during this treatment and the alkali metal hydroxide formed passes almost completely into the aqueous phase, leaving a solvent phase which is substantially free from inorganic compounds. The water used could, if desired, contain some acid which would neutralise some or all of the excess alkali. Preferably a slight deficiency of acid would be employed so that the final mixture remained alkaline. It is preferred that the amount of water employed should be merely just sufficient to dissolve the metal halide formed in the reaction. The use of a large excess of water should be avoided when using an alkanol which has an appreciable water miscibility.

The trialkoxypropene may be recovered from the alcohol phase by distilling 01f the alkanol for example under reduced pressure.

The trialkoxyprop-Z-enes of the present invention are valuable intermediates and for example react with ami-' dine compounds, such as guanidine, to give Z-substituted pyrimidines, such as Z-aminopyrimidine, Z-Amino-pyrimidine is itself an important intermediate in the production of sulfadiazine. 1:1:3-Trialkoxyprop-2-enes are also intermediates for photographic sensitizers, for which purpose they are condensed with a suitable pyrrole base according to British Patent 696,646.

In the examples the abbreviation w./W. stands for Weight by weight, and parts by weight bear the same relation to parts by volume as do kilograms to litres. Thus, an x% w./w. solution contains x parts by weight of solute in 100 parts by weight of solution.

Example 1 A mixture of 147.3 parts by weight of 2-chloro-1:1:3- tri-n-butoxypropane (0.5 molar proportion) and a 30% w./w. solution of potassium n-butoxide (1 molar proportion) in n-butanol was refluxed for 9 hours. The cooled product was extracted with 320 parts by volume of water and the washed oil layer was then distilled at 100 mm. mercury pressure to remove n-butanol and a little dissolved Water. The remaining oil was subsequently, distilled at 10-12 mm. mercury pressure without fractionation, to give a distillate containing 1:1:3-tri-n-butoxyprop-Z-ene (0.41 mole) in about purity. Fractionation of this distillate afforded the cisand transisomers of the tributoxypropene. The pure trans-isomer had a boiling point of 157/8 mm.', and refractive index 11 1.4380; the main bulk of the cis-isomer still contained a little of the trans-compound.

The 2-chloro-1:1:3-tri-n-butoxypropane used as starting material in the present example may be prepared as follows: I

m-chloroacrolein, obtained by reacting acrolein with aqueous hypochlorous acid andsteam distilling the resultant a-chloro-fi-hydroxy-propionaldehyde, is heated with an excess of n-butanol in the presence of a catalytic quantity of concentrated sulfurie acid,'while azeotropi- I eall y removing the water of reaction. f

, B mb e? p A mixture of a 35% w./w. solution of ota i m game-2.1

- 3 isobutoxide (1 molar proportion) in isobutanol and 2- chloro-lz3 tri-isobutoxypropane (0.5 molar proportion) was refluxed for 8 hours. The cooled reaction product was washed with 300 parts by volume of water, the oil layer separated, and the isobutanol distilled ofi from it at about 100 mm. of mercury pressure. The residual oil was flash-distilled at 10-12 mm. of mercury pressure to give a distillate containing 1:1:3-tri'isobutoxyprop-Z-ene (0.39 molar proportion), from which the pure tri-isobutoxypropene was recovered by fractionation. The purified material had a boiling point 138/ 13.5 min, and refractive index n 1.4321.

Example 3 A 35% w./w. solution of sodium isobutoxide in isobutanol containing 1 mole of sodium isobutoxide was refluxed for 8 hours with 145 parts by weight of crude 2-chloro-1: 1 :3-tri-iso-butoxypropanecontaining about 4% of 2-chloro-1:1-di-isobutoxy-prop-Z-ene. The cooled reaction product was extracted with water (500 parts by volume), the oil layer stripped free from isobutanol, and the residual material distilled, without fractionation at 12 mm. mercury pressure. The distillate contained 0.29 mole of 1 :1:3-tri-isobutoxyprop-2-ene.

Example 4 A 4.19% w./w. solution of acrolein in water was passed countercurrently with chlorine through a glass vertical reactor tube of capacity 20 parts by volume. The temperature of the reaction was maintained in the range -10 C. by means of brine coolant passing through a coil inside the reactor. The acrolein solution was fed at parts by volume per hour and the chlorine at such a rate-that the product overflowing contained a small excess of chlorine and no acrolein.

The product from the chlorhydrination was then fed at 10 parts by volume per hour to the head of a threeplate continuous distillation column. The plates of the column were modified so that at the feed rate employed the residence time of the liquid on each was /2 hour; the residence time of the liquid in the kettle was also /2 hour. The column was surmounted by a phase-separat ing stillhead, from which the heavier a-chloracrolein layer was continuously withdrawn while the aqueous layer was returned to the head of the column. The aqueous solution overflowing continuously from the kettle was run to waste. Under steady conditions, 2.637 parts by weight a-chloracrolein were obtained per 40 parts by volume of feed, this being a 97.4% yield of the m-chloracrolein based on acrolein fed to the chlorhydrination.

A mixture of 4.525 parts by weight of a-chloracrolein, 22.2 parts by weight of isobutanol and 0.27 part by weight of concentrated sulphuric acid was fed to the mid-point of a continuous fraotionating column, provided with a decanting stillhead. From the stillhead the water-rich lower layer of isobutanol/Water azeotrope was removed, whilst the upper isobutanol-rich layer was returned to the column. The dehydrated product from the base of the still was allowed to overflow into a second kettle, the feed rate being such that the total time of residence in the system was 4 hours. 24.03 parts by weight of this crude product containing approximately equal weights of the mixed acetals (1:123-tri-isobutoxy-Z-chloropropane, 1:1- di-isobutoxy-Z-chloroprop-Z-ene) and unchanged isobutanol was mixed with 61 parts by Weight of 21% w./w.

potassium isobutoxide/isobutanol solution. The mixture was fed to the mid-point of a continuous fractionating column, from the head of which was distilled ofi a quantity of isobutanol equivalent to (a) the unchanged isobutanol from the acetalisation process and (b) a further quantity required to increase the concentration of the isobutoxide from 21 to 35% by weight. The overflow from the still kettle passed to a second kettle and this feed rate was such that the total residence time in the system as. 6 ho s.

When steady conditions hadbeen established, 25.26 parts by weight of product from the second kettle were stirred mechanically with 12.15 parts by weight of Water. The upper oil layer which separated was then passed through a climbing film evaporator at about 40 parts by volume per hour with a wall temperature of about and an internal pressure of 17 mms. of mercury. There was thus obtained a distillate (16.91 parts by weight) consisting mainly of isobutanol and a residue of 7.87 parts by weight. Of the residue, 7.74 parts by weight was continuously distilled at a pressure of 116-130/5 mms. of mercury. The distillate (6.35 parts by weight) contained, by analysis, 58.7% by weight of 1:1:3-tri-isobutoxyprop-Z-ene, the yield being 57.6% of theory from ct-chloracrolein.

Example 5 A mixture of 2-chloro-1:1:3-tri-isobutoxypropane (73.7 parts by weight) and a solution of potassium (19.5 parts by weight) in Z-ethylhexanol (325 parts by weight) was refluxed for 6 hours. The base temperature was 194.

The cooled product was washed with water (250 parts by volume) and distilled under reduced pressure, three fractions being collected as follows:

(1) Boiling point ca. 40/ 10 mm. of mercury (2) Boiling point 5274/0.7 mm. of mercury (3) Boiling point 74-160/0.7 mm. of mercury The non-aqueous portion of fraction (1) was combined with fraction (2) giving 300 parts by weight of material containing 2.5% by weight of fi-alkoxyacrolein acetal (calculated as fl-isobutoxyacrolein di-isobutyl acetal). Fraction (3) (67.9 parts by weight) contained 67.5% by weight of the acetal and the total yield was thus 82.7% of the theoretical.

The residue from the distillation and the water-washings were analysed for chloride ion: the amount found showed that dehydrochlorination had been 99.5% complete.

Portions of fraction (3) were condensed with guanidine hydrochloride when Z-aminopyrimidine was obtained in 94% yield (based onthe purity of 67.5

We claim:

1. A process for the production of a 1:1:3-tria1koxyprop-Z-ene which comprises reacting at an elevated temperature a 1:1:3-trialkoxy-Z-chloro-propane with an alkali metal alkoxideot 4 to 8 carbon atoms in solution in an alkanol of 4 to 8 carbon atoms, the alkoxide and the alkanol each having a straight chain of at least 3 carbon atoms, wherein the product resulting from the reaction is treated with suflicient water to hydrolyze any excess alkoxide and to form an aqueous phase containing the formed alkali metal halide in solution and an alkanol phase, and recovering the 1:1:3-trialkoxyprop-2-ene from the alkanol phase.

2. A process according'to claim 1 for the production of 1:1:3-tri-n-butoxyprop-2-ene wherein 1:1:3-tri-n-butoxy-Z-chloropropane is reacted with potassium n-butoxide in n-butanol solution.

3. A process according to claim 1 for the production or" 1:1z3-tri-isobutoxy-prop-Z-ene wherein 1:1:3-triisobutoxy-2-chloropropane is reacted with potassium isobutoxide in iso-butanol solution.

4. A process for the production of a 1:1:3-trialkoxyprop-Z-ene in accordance with claim 1 wherein the 1:1:3- trialkoxy-2-chloropropane is contained in the crude product obtained by treating tz-chloro-acrolein with a theoretical excess of the alkanol in the presence of a catalytic amount of sulfuric acid at an elevated temperature while azeotropically removing the Water of reaction.

5. A process according to claim 1 wherein the alkali metal alkoxide is an alkali metal butoxide.

6. A process according to claim 1 wherein the alkali metal alkoxide is a-potassium alkoxide.

7. A process according to claim 1 wherein the reaction 6 is carried out using the alkali metal alkoxide in solution References Cited in the file of this patent in the corresponding alkanol. UNITED STATES PATENTS 8. A process according to claim 1 wherein the alkoxy 2288-211 Schulz et a1. June 30 1942 groups of the startmg material correspond to those of the alkoxide and the alkanoi. 5 2374078 cofiman "T 1945 9. A process according to claim 1 wherein the reac- OTHER REFERENCES tio i carried out a temperature in the range to McElvain et al.: J. A. c. 5., vol. 64 (1942 p. 1966.

160 C. Fieser et al.: Organic Chemistry (1950), p. 59. 

1. A PROCESS FOR THE PRODUCTION OF A 1:1:3-TRIALKOXYPROP-2-ENE WHICH COMPRISES REACTING AT AN ELEVATED TEMPREATURE A 1:1:3-TRIALKOXY-2-CHLORO-PROPANE WITH AN ALKALI METAL ALKOXIDE OF 4 TO 8 CARBON ATOMS IN SOLUTION IN AN ALKANOL OF 4 TO 8 CARBON ATOMS, THE ALKOXIDE AND THE ALKANOL EACH HAVING A STRAIGHT CHAIN OF AT LEAST 3 CARBON ATOMS, WHEREIN THE PRODUCT RESULTING FROM THE REACTION IS TREATED WITH SUFFICIENT WATER TO HYDROLYZE ANY EXCESS ALKOXIDE AND TO FORM AN AQUEOUS PHASE CONTAINING THE FORMED AKLALI METAL HALIDE IN SOLUTION AND AN ALKANOL PHASE, AND RECOVERING THE 1:1:3-TRIALKOXYPROP-2-ENE FROM THE ALKANOL PHASE. 